The trend of smart hardware and portable device makes miniaturized actuators development more motivational and intriguing in modern industries. Applications like smart robot and auto-stabilized gimbal require simultaneous controls in multiple degrees of freedom (DOF). In a conventional actuator system design, it takes multiple single-DOF actuators being combined into one assembly to achieve multi-DOF in forms of translation and/or rotation. However this approach inherently hinders further compactness and miniaturization of the actuator design.
Alternatively, mechanisms with intrinsic multi-DOFs movements capability within a single joint, such as ball-joint-like (spherical) actuators, show advantages in creating a more compact and elegant multi-DOF actuator system design. Several spherical actuator designs have been demonstrated during the last two decades, including permanent magnet spherical motor, spherical induction motor, variable-reluctance spherical motor, and ultrasonic spherical motor, etc. These actuators can provide position and/or velocity controls in two DOFs (pan and tilt), or even three DOFs (pan, tilt, and spin) by utilizing electromagnetic forces.
Taking permanent magnet spherical motor as an example, such actuator consists of a rotor with multiple number of permanent magnetic poles, and a stator with multiple number of electromagnetically driven coils. As control current signals go through the coils, magnetic forces and torques are generated to orientate the rotor towards its minimal system potential energy. Additional sensors such as encoders, Hall effect sensors, and magnetic field intensity sensors, etc. can be applied to measure and update the orientation and/or rotational speed of the rotor relative to the stator, and inverse kinematics can be used to update the control current signals to make it a closed-loop system.
Although showing superiority comparing to brute force combination of single-DOF actuators, a state-of-the-art spherical actuator still needs independent control and driving signals on each (or each pair of) electromagnetic coil(s). As the requirements of orientation/rotational speed control become more precise and strict, greater number of coils is desired, which leads to larger and more bulky electronic driving circuit design. This becomes one of the major barriers in making a miniaturized multi-DOF actuator design, counteracting its advantages in mechanism aspect.
What is needed is a smarter control strategy that requires fewer number of phases (or channels) of electromagnetic control signals, which will be put forth as solutions in the next section.
The present invention is aimed at one or more of the problems identified above.